That's not going to work very well, you'll get a mixed cohort of people reporting actual fraud and deceptive practices (the desired group) and people who were just pissed off because they didn't get the support they needed (a legitimate complaint, but not as relevant to the issue of fraud) or had negative personal interactions (not such a legitimate complaint, as they might have been the problematic person).

I think the same issues affect Glassdoor, but it didn't stop the site being a hit. Just let people speak, and the audience judge by themselves and filter the outlier report from the problematic person.